1. Field of the Invention
The present invention relates to sliding means that have been extensively used in machines and instruments as diverse as semiconductor manufacturing apparatus, machine tools, industrial robots, conveyors and others. It is more particularly concerned with a sliding means with built-in moving-magnet linear motor, in which an armature winding is arranged in a stationary bed while a field magnet is installed in a moving table.
2. Description of the Prior Art
In recent years, multi-axis stages and moving mechanisms employed in the diverse technical fields as described above have required more and more sliding means, which are compact or slim in construction and light in weight, and moreover able to operate with high propulsion, high speed and high response to provide high speed travel and accurate position control for works, tools, articles and instruments. Linear motors commonly used in the sliding means involve two broad types. The first, called moving-coil linear motor, has a stator of field magnet mounted on a stationary bed, and moving-armature windings arranged on a table movable lengthwise of the bed in sequence one after another such that they lie a preselected phase angle. The second, called moving-magnet linear motor, has a stator of armature windings arranged lengthwise over the entire length of a bed, and a moving-field magnet of permanent magnet arranged on a table movable in a sliding manner along the length of the bed.
Japanese Patent Laid-Open No. 322232/1996 discloses a linear motor installed in a knitting machine to drive a knitting needle in reciprocating motion. The liner motor is comprised of a plurality of built-in moving-coil liner motor units each of which has a moving assembly composed of a backing plate made therein a window, a resilient sheet member fixed on any one side of the backing plate with adhesive, and exciting windings, for example three windings, arranged on any one surface of the sheet member in a manner to be partly accommodated in the window. The exciting winding is made in the form of flat ellipse where the axial direction of the winding extends thickness-wise of the linear motor unit. The moving assembly is arranged for linear movement between stator assemblies confronting one another, each of which is composed of a backing plate made of ferromagnetic material such as steel, and a plurality of permanent magnet, for example six pieces arranged on the backing plate in juxtaposition along the traveling direction of the moving assembly. The construction in which the exciting windings are accommodated in the associated window in the backing plate reduces the overall thickness or height of the moving assembly. Linear displacement-measuring means is composed of a linear scale extending along the moving direction of the moving assembly, and a sensor head installed on any one of the confronting stator assemblies.
A dc linear motor is disclosed in Japanese Patent Laid-Open No. 47239/1996, in which any one of forward and aft end poles in the field magnet is made insensitive to a pole discriminating element. With the do linear motor recited just above, a moving table is provided on the underside thereof with a magnet yoke, underneath which a field magnet is arranged in opposition to primary armature windings mounted on a stationary bed. The field magnet is made in the form of rectangle in which unlike poles or N-, S-poles are arranged alternately along the fore-and-aft direction thereof. Any one of the forward and aft end poles is made insensitive at a surface opposing to a Hall-effect element to discern the end of the field magnet for monitoring a position of the moving table. This makes it possible to reduce a deviation in number of the coil sides of the armature windings, which might contribute to really generating propulsion, thus realizing the steady propulsion.
A moving-magnet brushless dc linear motor is disclosed in Japanese Patent Laid-Open No. 298946/1989, in which a semiconductor rectifier is arranged for each coil, and two sets of three-phase coil groups are arranged to provide a linear motor of three-phase conduction system.
A sliding means adapted to be used for machine tools and industrial robots is disclosed in Japanese Patent Laid-Open No. 266659/1997, which is a senior copending application of the present applicant. The prior sliding means includes a driving source made of an electromagnetic linear actuator and a built-in moving-magnet uniaxial linear motor to control with precision a position of a driven article. With the prior sliding means cited just above, an electromagnetic linear actuator is arranged between a moving table and stationary bed of steel or magnetic material and at least any one of the table and the bed is constructed to serve a part of magnetic circuit of the electromagnetic linear actuator, concretely the function of either magnet yoke or coil yoke. The prior sliding means has no need of providing separately yokes for establishing magnetic circuit, which might make the sliding means bulky, thus reduced in the number of parts required, and made inexpensive in production cost and slim in construction.
The sliding means disclosed in the above Japanese Patent Laid-Open No. 266659/1997 will be explained below, with referring to FIGS. 18 and 19. A sliding means 51 with an built-in linear motor is composed of a stationary bed 52 and the moving table 53, both of which are made of magnetic material such as steel to serve the function of magnetic circuit, or magnet yoke and coil yoke, thereby rendering the linear motor small or compact in size. The sliding means 51 with built-in linear motor has the stationary elongated bed 52, and the moving table 53 mounted on the bed 52 for linearly reciprocating movement lengthwise of the bed 52 by virtue of linear motion guide units 54. The linear motion guide units 54 are comprised of two track rails 55 arranged on the bed 52 in parallel with each other, and four sliders 56 fitting over the associated track rail 55 for sliding movement. In the linear motion guide units 54, load raceway areas are provided between confronting raceway grooves, one of which is formed on lengthwise sides of the track rails 55 while the counterpart is formed on the sliders 56. The sliders 56 are allowed to move with smooth along the track rails 55 as rolling elements run through the load raceway areas. The table 53 is bored with holes 58 through which screws fit to fix a work on the table 53.
An end block 61 and a connector block 62 are secured to the lengthwise opposing ends of the bed 52, each to each end, with fixing bolts 63, 64 to define a tolerable range of operating stroke of the table 53. The bed 52 is made with holes 65 through which bolts 66 fit to anchor the bed 52 to a platform.
An armature 70, which is a primary side of the sliding means 51, is comprised of a coil board 71 and eight pieces of armature windings 72 arranged on the underside of the coil board 71 in juxtaposition along the moving direction of the table 53. The bed 52 is recessed lengthwise at 73 on the upper surface thereof, where the armature 70 is accommodated through an insulating film 74. Hall-effect elements 75 are arranged on the coil board 71 in conjunction with the armature windings 72, each to each winding. The Hall-effect elements 75 are to issue a signal in response to an amount of magnetic flux created by a secondary field magnet 90, which is detected when the field magnet 90 approaches the Hall-effect elements 75. Excitation of the armature windings 72 is controlled depending on the signal issued out of the Hall-effect elements 75. The armature 70 is jointed to the bed 52 by means of machine screws 76 fitting through spacers 77, which make abutment at their opposing ends against both the bed 52 and the coil board 71 at locations offset widthwise of the bed 52 between any two adjacent armature windings 72 from one another.
The bed 52 is also made with a recess 79 at the underside opposite to the upper recess 73. A driving board 80 is received in the lower recess 79 through an insulating film 81. The driving board 80 is to apply electricity to the armature windings 72, and mounted with a driving circuit 82 composed of diverse electronic components. The driving board 80 is connected with the coil board 71 via connectors 83, 84 extending through a hole 85 bored vertically through the bed 52. In addition, the lower recess 79 in the bed 52 is closed with a cover 86.
The field magnet 90, which is the secondary side of the linear motor, is installed in a recess 92 formed in the table 53 and secured to the underside of the table 53. The field magnet 90 is composed of platy magnets 91 arranged such that unlike poles or N-, S-poles on the platy magnets 91 alternate along the moving direction of the table. The table 53 mounted with the platy magnets 91 provides a magnet yoke forming a part of magnetic circuit, while the bed 52 provides a coil yoke for each armature winding 72, which also forms a part of magnetic circuit. When each armature winding 72 carries the preselected current, a thrust force is created between the primary and secondary sides on the basis of Fleming""s rule to drive the table 53 integral with the secondary field magnet 90 with respect to the bed 52 in a sliding manner by virtue of the linear motion guide units 54.
To determine the reference position of the table 53 with respect to the bed 52, a Hall-effect element 97 is installed inside the second armature winding 72 from the left. The reference position may be identified by a signal issued at a time when the Hall-effect element 97 has detected the leftmost platy magnet 91 in the field magnet 90. Besides, two Hall-effect elements 98, 99 are attached to the coil board 71 inside the leftmost and rightmost armature windings 72, each to each winding, to provide limit sensors that ensure keeping the table 53 from travelling over the tolerated range of moving stroke. Each Hall-effect element 98, 99, when the table 53 has traveled over the tolerated range of the operating stroke, may respond to any associated pole at the leftmost and rightmost extremities of the field magnet 90 to issue a signal reporting the accidental event where the table has run away from the desired stroke. In order to monitor the relative location of the table 53 to the bed 52 in the sliding means 51, the table 53 is provided at one lengthwise side thereof with a magnetic linear scale 95 in which unlike magnetic poles (N-, S-poles) are arranged alternately with a fine pitch along the moving direction of the table 53, while the bed 52 has a sensor head 96 responsive to the magnetic scale 95.
In the sliding means 51 with built-in linear motor constructed as stated earlier, there is employed a system in which electric conduction is controlled every each armature winding 72 and, therefore, both the driving board 80 and the driving circuit 82 are built in underneath the bed 52. This system makes the sliding means complicated and bulky in construction. Besides, the linear scale is made of magnetic scale.
Modern advanced machinery and instruments such as semiconductor manufacturing machines, measuring instruments, assembly machines, and so on much desire sliding means that is able to operate accurately with high speed, thereby providing a position control mechanism suitable for clean room and high in propulsion, operating speed and responsibility, with even more compact as compared with the conventional sliding means.
By the way, in conventional sliding means with built-in moving-magnet linear motor in which a table is arranged on a bed for sliding movement through the linear motion guide units, the construction has been employed in which the current flowing through the armature winding installed in the bed interacts with magnetic flux created by the field magnet on the table to generate an electromagnetic force to drive the field magnet together with the table relatively to the bed, and a magnetic detector element such as Hall-effect IC, and so on is mounted on the bed to monitor the field magnet arranged on the table, thereby to control a relative position of the table to the bed. The provision of a magnet only for the position control causes the increase of production cost. Consideration has been thus given to getting the field magnet for table propulsion to function as the magnet for position control.
Nevertheless, in the field magnet in which unlike poles are arranged alternately along the moving direction of the table, magnetic flux distribution is kept closely concentrated between any two adjacent poles opposite in polarity, but at, the forward and aft end poles is diverged outwardly of field magnet. For instance, a position where the lengthwise field density is zero swerves much outwardly of the forward and aft end poles of the field magnet. This means that the magnetic detector element could not sense the accurate positions of the forward and aft end poles. To cope with this, it has been needed to rectify the magnetic flux created at the end poles to make it possible to identify the positions of the forward and aft end of the field magnet with as same accuracy as in the detection of a boundary between the adjacent poles opposite in polarity in the field magnet.
The present invention has as its primary object to overcome the subject stated earlier and more particular to provide a sliding means with built-in moving-magnet linear motor, in which a magnetic sensor element is allowed to sense accurately a position of any end pole of a field magnet with no provision of an extra magnet only for the position control. To this end, the present invention contemplates to rectify a distribution pattern of magnetic flux created at any one end pole of the field magnet, which is commonly rendered N-polar in light of most current magnetic sensor elements designed to sense N-pole, to the same distribution pattern as found at a boundary between the adjacent poles opposite in polarity in the field magnet.
The present invention relates to a sliding means with built-in moving-magnet linear motor, comprising a bed constituent one of paired members arranged for sliding movement relatively of each other, a table constituent another of the paired members, which is arranged movable lengthwise of the bed in a sliding manner with respect to the bed, a field magnet having unlike magnetic poles juxtaposed alternately in polarity in a moving direction of the table, an armature winding assembly having armature windings installed on the bed in opposition to the field magnet, a magnetic sensor elements installed on the bed in opposition to the field magnet to monitor a strength and direction of magnetic flux, and an auxiliary magnet arranged adjoining to any one of forward and aft magnetic end poles of the field magnet and magnetized in a polarity unlike the associated end pole, wherein a current in each armature winding interacts with magnetic flux created by the field magnet to produce an electromagnetic force to render propulsion to the field magnet to drive the table with a desired position control, and the auxiliary magnet makes up for the magnetic flux at the end pole of the field magnet, thereby making the magnetic sensor element detect an accurate position of the field magnet.
With the sliding means constructed as recited earlier, the electric current existing in the armature windings interacts with the magnetic flux created in the field magnet to generate the electromagnetic force to provide the propulsion driving the table with respect to the bed.
In an aspect of the present invention, a sliding means is disclosed, wherein the auxiliary magnet serves to rectify the strength and direction of the magnetic flux outside a boundary of the end pole of the field magnet to the roughly same strength and direction as the magnetic flux found at a boundary between any two adjacent magnetic poles in the field magnet.
The magnetic sensor element installed on the bed in opposition to the field magnet detects the strength and direction of the magnetic flux created by the field magnet, controlling the electric current in the armature windings to thereby drive the table in a sliding manner to a desired position. The auxiliary magnet serves to rectify the magnetic flux pattern at the end pole of the field magnet, which might otherwise deviate outwardly, thereby providing the same strength and direction as in the magnetic flux found at a boundary between any two adjacent magnetic poles in the field magnet. This makes it possible to sense any end pole of the field magnet with the same accuracy as at the boundary between the two adjacent poles in the field magnet.
In another aspect of the present invention, a sliding means is disclosed, wherein both the bed and the table are made of steel of ferromagnetic material. As a result, the bed may serve as a coil yoke while the table may serve as a magnet yoke, for the sake of which the linear motor comprised of the armature winding assembly and the field magnet may be made compact or slim in overall construction, with even highly efficient electromagnetic reaction. Moreover, the field magnet is made of rare earth magnet such as neodymium or the like and has therein the magnetic poles of a multiple of 4, which are juxtaposed alternately in polarity. The field magnet stated just earlier is effective in raising flux density, thereby providing high propulsion (=currentxc3x97flux density). This makes it possible to ensure much high-speed movement, responsibility and accurate position control.
In another aspect of the present invention, a sliding means is disclosed, wherein the armature windings are divided into at least two winding groups, each of which includes three armature windings carrying each phase current for three-phase conduction system, and the total number of the armature windings is at least the number of the magnetic poles in the field magnet. According to the sliding means stated just above, there is no need of providing onboard driving circuits underneath the bed as opposed to the prior construction in which conduction systems are individually prepared for every armature winding. Thus, the driving circuits can be moved from the sliding means to the driver side of driving means. Consequently, the three-phase conduction system in which each armature winding carries each phase current makes it possible to remove the driving circuits from the sliding means to the exterior driver, whereby the sliding means in itself may be reduced in overall height.
In another aspect of the present invention, a sliding means is disclosed, wherein the field magnet has therein four magnetic poles while there is provided six armature windings and the table has a fore-and-aft length that affords to ensure the space for the five magnetic poles. According to the aspect stated above, the sliding means may be made compact or slim in overall construction, with even ensuring the traveling range needed in the practical sliding means.
In a further another aspect of the present invention, a sliding means is disclosed, wherein the auxiliary magnet is made less in width in the sliding direction than a width of a coil side of the armature winding to reduce any effect on propulsion rendered to the table. As will be apparent to those skilled in the art, the electric current in the coil sides of the armature winding creates magnetic flux, which in turn interacts with magnetic flux generated by the field magnet to produce the propulsion to force the table. Thus, the auxiliary magnet made less in width in the sliding direction than a width of a coil side of the armature winding is effective to minimize the influence owing to the interaction of the armature windings with the auxiliary magnet on the propulsion given to the table from the field magnet.
In another aspect of the present invention, a sliding means is disclosed, wherein the table is provided with an origin mark to define an origin of the table, and a sensor magnet arranged adjoining to the magnetic end pole fore-and-aft opposite to the auxiliary magnet and magnetized in a polarity unlike the associated magnetic end pole, while the bed is provided with an origin sensor to detect the origin mark, and the armature winding assembly is mounted with a before-the-origin sensor to respond the sensor magnet at a before-the-origin position just before the origin sensor detects the origin during a linear movement of the table along the bed, and a limit sensor to respond any one of the magnetic end pole and the sensor magnet when the table reaches any dead end position of a tolerated stroke range.
As the forward and aft end poles of the field magnet are unlike in polarity, the limit sensors and the before-the-origin sensor should be necessarily set to respond the unlike polarities. Although any one end pole corresponds to any one of the limit sensors, another end pole is unlike in polarity so that there is no need of the polarity setting stated just above. As opposed to the above, the sensor magnet of unlike polarity is provided. Thus, both the limit sensors and the before-the-origin sensor detect the sensor magnet thereby making it possible to control the table in its position and traveling stroke.
In another aspect of the present invention, a sliding means is disclosed, wherein the sensor magnet is arranged outside the field magnet and made less than and equal in length to a half the field magnet to reduce the effect on the propulsion exerted on the field magnet. In order to keep negligibly small the effect of the sensor magnet on the propulsion exerted to the table, consideration must be given to the shape of the sensor magnet and the relative location of the sensor magnet to the field magnet.
In a further aspect of the present invention, a sliding means is disclosed, wherein the sensor magnet is made of ferrite magnet. Compared with the rare earth magnet, ferrite magnet is weak in magnetic force and, therefore, the adverse effect on the propulsion exerted to the table may be made less.
In another aspect of the present invention, a sliding means is disclosed, wherein the auxiliary magnet is magnetized in S-pole, the magnetic pole adjacent to the auxiliary magnet is in N-pole, while the sensor magnet is magnetized in N-pole and the magnetic pole adjoining to the sensor magnet is magnetized in S-pole. Thus, the magnetic sensor element can read the position of the table.
In another aspect of the present invention, a sliding means is disclosed, wherein an encoder to monitor a position of the table in the sliding direction with respect to the bed is an optical encode, which is comprised of an optical linear scale arranged on the bed and a sensor installed on the bed in opposition to the optical linear scale to read the optical linear scale. The optical encoder, since tough to be affected by the relative changes of the sensor with the scale, is preferred for highly accurate requirements. Moreover, selection of the optical encoder rather than the magnetic encoder contributes to improvement in resolution, ensuring highly accurate position control. The optical linear scale of the optical encoder is arranged on the underside of the table while the sensor element to read the linear scale is installed in the bed. Thus, there is no sensor cord or line moving in conjunction with the travel of the table. The construction is effective in keeping the sliding means itself low in the occurrence of dust and dirt, thus realizing clean environment.
In another aspect of the present invention, a sliding means is disclosed, wherein the magnetic sensor elements are Hall-effect ICs arranged in the armature windings, each to each winding. These magnetic sensor elements or Hall-effect ICs are available at considerably inexpensive cost and easily arranged in place by assembling together at the time of fabricating the armature winding.
In another aspect of the present invention, a sliding means is disclosed, wherein the table is provided with an end plate at a position adjoining the auxiliary magnet to keep the magnetic flux established in the field magnet against leakage. As the end plate keeps the magnetic flux established in the field magnet from leakage out of the associated end of the table, anything approaching the table may be protected against magnetic affection.
In a further another aspect of the present invention, a sliding means is disclosed, wherein the armature windings are accommodated in a recess cut in the bed along the sliding direction of the table, and linear motion guide units are interposed between the confronting table and bed and arranged on widthwise opposing sides of the recess along the moving direction of the table. The armature windings are accommodated in the recess cut in the bed. Thus, the bed may be made as thin in height as possible so that the sliding means is made much slim in overall height. The linear motion guide units arranged spaced across the recess in parallel along the sliding direction of the table help ensure steady travel of the table with respect to the bed. The field magnet is allowed to fit in a clearance that is left between the widthwise-opposed linear motion guide units interposed between the confronting table and bed. Besides, the encoder may be arranged on the bed and the table outside any one of the linear motion guide units.
In another aspect of the present invention, a sliding means is disclosed, wherein the armature windings are mounted on a coil board to cover the recess, so that the armature windings are arranged in a flat form that is fitted snugly in the recess. The armature winding assembly composed of the coil board and flat armature windings is made as thin as possible in thickness to be able to fit in the recess cut in the bed. Each the armature winding is composed of turns wound in the form of rectangle and a resinous core molding the turns therein. The core of molded resin serves well to preserve the shape of the armature winding.
In another aspect of the present invention, a sliding means is disclosed, wherein the bed has an end block at any one of the forward and aft ends thereof, and has a connector block at another of the forward and aft ends, the connector block having an electric power cord to be connected to the armature windings and a sensor line to be connected to the sensor element of the encoder, and elastic stoppers are mounted on the blocks, each to each block, to buffer collision with the table. If the table were moved beyond the tolerated stroke range with respect to the bed, the elastic stopper inside the end block or the connector block would buffer the collision with the table to protect the sliding means against breakage.
With the sliding means constructed as stated earlier, the auxiliary magnet behaves in a manner that rectifies the flux pattern created outside the magnetic end pole of N-pole in the field magnet to the same flux pattern as found at the boundary between the adjacent poles opposite in polarity in the field magnet, thus making it possible to identify the accurate position of the table with respect to the bed.
The sliding means of the present invention, therefore, helps ensure the improvements in much high-speed movement, responsibility and accurate position control of the table with respect to the bed. According to the present invention, moreover, there is no need of providing a magnet only for the position control and the detection of the table position can be realized by relying instead on the existing field magnet and magnetic sensor element. This results in lowering the production cost. In addition, the sliding means of this invention, as being made as compact as possible in size, realizes space saving in production, storage, conveying, installation and use thereof, making for an improvement in working environment, and further providing position control mechanism that is suitable for clean room and high in propulsion, operating speed and responsibility.